The PPP's executive board had earlier today agreed to nominate Somchai, the brother-in-law of self-exiled Thaksin Shinawatra, as its candidate to be next prime minister.
Somchai was nominated to replace Samak Sundaravej at an executive meeting of the People Power Party (PPP), party leader Kuthep Saikrachang said.
Whereas Somchai's nomination is expected to receive support from coalition allies, he will run straight into trouble.
The People Alliance for Democracy has declared its rejection of his nomination. The ruling People Power Party, meanwhile, is now in danger of a rebellion by a key faction led by Newin Chidchob.
Newin's faction controls 73 MPs, who declared in the afternoon that they would not vote for Somchai despite his nomination by the PPP's executive board.
The Constitution Court disqualified Samak as prime minister on Septebmer 9 for violating the constitution. Somchai then became acting prime minister and he has scored a major political point by lifting the state of emergency which was imposed by Samak.
Kuthep insisted that Somchai has received the most support from the PPP leadership. "The PPP executives decided the candidate with the best qualifications to become the prime minister was Somchai," said Kuthep.
Somchai's nomination has been forwarded to the party's five coalition partners for consideration. Parliament is scheduled to meet Wednesday to vote on the next prime minister.
Somchai is brother in law of former prime minister Thaksin. He's married to Thaksin's younger sister; Yaowapa.
The PAD rejected Somchai's nomination on grounds that he is too close to former prime minister Thaksin.
Chamlong Srimuang, one of PAD leaders, warned today that Somchai could be a "bigger Thaksin proxy" than Samak.
Anti-government protesters initially said their goal was to remove Samak. Now they are saying they will not accept any successor from his party or any successor considered an ally of Thaksin.